The invention relates to a semiconductor laser having a semiconductor body comprising a substrate of a first conductivity type and a layer structure disposed thereon and comprising successively at least a first passive layer of the first conductivity type, a second passive layer of the second opposite conductivity type and an active layer located between the first and second passive layers and having a pn junction which can produce (at a sufficiently high current strength in the forward direction) coherent electro-magnetic radiation in a strip-shaped region of the active layer located within a resonant cavity, the first and second passive layers having a lower refractive index for the radiation produced and a larger band gap than the active layer, while a current-limiting blocking layer is provided, which at the area of the active region has a strip-shaped interruption, two grooves being provided on either side of the active region and extending from the upper side of the second passive layer through the active layer into the first passive layer, which grooves are at least partly filled by the blocking layer. Semiconductor lasers are important in many fields of technology and are used in many applications.
A semiconductor laser of the kind described above is generally known under the designation DCPBH (Double Channel Planar Buried Hetero-structure) laser and is disclosed in European patent application No. EP 0111650. A disadvantage of these lasers is a strong temperature dependence of the threshold current.
InGaAsP/InP double hetero-junction (DH) lasers in particular have strongly increasing threshold current values with increasing temperature. This is partly due to the fact that charge carriers enclosed in the active layer thermally leak away to the passive layers.
I.E.E.E. J. of Quantum Electronics (QE 19, August 1983, 1319-1326) discloses semiconductor lasers provided with an additional (second) active layer. These so-called DCC (Double Carrier Confinement) lasers have a high temperature stability for InGaAsP/InP lasers. A disadvantage of DCC lasers, however, is that they have a comparatively high threshold current value. For a DCC laser, the threshold current value is of the order of 100-300 mA, while for a DCPBH laser this value is of the order of 10-30 mA.